Sitting in an air-conditioned office in Brasilia, Brazil's modernist federal capital that always has an unreal feel to it, we found it difficult not to be impressed. Or maybe, after so many depressing stories about the destruction of the rainforest, we just wanted to believe what we were being told. We were both beguiled by the vision so powerfully presented to us.

"A new era is beginning for the Amazon," said Tasso Rezende de Azevedo, the youthful head of Brazil's National Forest Programme, running a hand through his thick, brown hair. Bringing up on his computer a bewildering array of maps and aerial photos, he went on: "Today, thanks to modern satellite technology, we have instant information. We know almost immediately when someone is illegally cutting down the forest and we can send in one of our teams to arrest those responsible. From now on, loggers and farmers will have to obey the law."

Tasso belongs to a young Brazilian generation of environmental technocrats who have a fervent belief in the power of technology. Under the leadership of Marina Silva, the charismatic environment minister, who herself comes from the Amazon, they have developed an ambitious strategy for ending deforestation, now running at 1.3 million hectares a year, making Brazil the fifth largest global contributor to greenhouse gases. At the centre of this strategy lies a vast mosaic of conservation units, stretching across the heart of the Amazon Basin from north to south and already covering some 20 million hectares (an area the size of England and Scotland together), with more units planned.

The idea is that these reserves will act as a buffer and stop the human predators - the land-grabbers, illegal loggers, cattle ranchers and soya farmers - moving into the western Amazon, which is still largely untouched.

Some of these are old-fashioned nature parks, where no human activity is permitted. Others are so-called "extractive reserves" for the Amazon's long-term inhabitants such as the ribeir inhos (riverside dwellers, mainly descen ded from 19th-century rubber tappers or from runaway slaves). Yet others, created under Brazil's Project for Sustainable Development (PDS), are for the Amazon's shifting population of former gold prospectors, dam workers and landless families that have invaded indigenous reserves. Key to the success of all these conservation units are Tasso's satellite images, which will allow the government to ensure that only permitted, sustainable economic activity is undertaken.

But can it work? During 30 years of visiting the region, we have witnessed the relentless advance of the agricultural frontier ever deeper into the Amazon forest. Dared we hope that the destruction might be ending? We visited Santarém, an old port built by the Portuguese, where the mighty Tapajós tributary meets the even mightier Amazon River.

This area is being ransacked for hardwoods (especially ipê, now that mahogany, once known as green gold, has been exhaustively logged and exports banned) and planted with soya, the international wonder crop, fed to cattle all over the world. The riverfront, lined by trading and passenger boats that ply the local waters, is now overlooked by an ungainly soya terminal, built by the giant US commodities trader Cargill. If the government's policies were starting to bite here, then a new era really would be dawning.

We hired a 4x4 to visit Renascer, one of the government's new sustainable projects, situated about 200 kilometres south-east of Santarém. According to figures published at the end of last year by the National Institute for Rural Settlement and Agrarian Reform (Incra), 360 families have been settled here. To reach the settlement, we travelled through dense forest, skidding and sliding along dirt roads made as slippery as soap by recent rains. High up in the jungle canopy, we caught a glimpse of a pair of arara-azuls, a species of endangered macaw almost exclusively found in Brazil. Occasionally, a tapir or an agouti ran across the track. What became clear as we travelled further into the forest and passed countless loggers' tracks leading off either side of the road is that Renascer's 44,000 hectares (109,000 acres) had already been plundered for hardwoods.

We saw no sign of human life as we drove deeper into the settlement. At the end of the road we found several abandoned huts, strewn with discarded clothing. On one hung a hand-painted sign that read, somewhat forlornly, "Agro-Extractive Reserve Renascer, PDS". But where were the settlers? The only people we met within the settlement area were two men and a woman who had moved in on their own initiative, planting cassava between tree stumps in an area cleared by the loggers and rearing ducks in a stream. Having plundered the area, the loggers had moved further into the forest. "We can still hear the whine of chainsaws in the distance," one of them said.

Corrupt officials

On our return to Santarém and after talking to government officials, researchers and settlers, it became obvious that loggers have invented a scam to continue illegal logging. Under the terms of a PDS, settlers can clear one-fifth of the area they are allocated, while the remaining four-fifths goes to a collective forest reserve to be used for renewable activities, such as collecting Brazil nuts, extracting oil from andiroba trees, and sustainable logging. As the government tightens its control over logging, demanding proper forest-management projects and legal titles to the land, bandit loggers who have neither have found the weak spot in the new strategy. They have gone into partnership with corrupt officials within Incra, which authorises and administers the settlements, and have set up fake community organisations to run PDSs. Some of these have become facades behind which the loggers carry on plundering the forest.

Many innocent people are caught up in the scam. We discovered that a few years ago one logger had enticed some 80 people, desperate for a plot of land, to join his fake community organisation. He had taken them by lorry to Renascer to have a look at the land and dumped them there. But Renascer, set up with the interests of the loggers in mind, is located in difficult, hilly terrain. Marooned in this remote area, the would-be settlers began to get hungry and grew frightened after a few days. They started to trudge back to Santarém on foot. After walking 27 kilometres, they came to the nearest house, built by a soya farmer, who gave them food and water and even drove the eldest couple, in their late sixties, in his jeep back to Santarém. All that is left of this failed experiment is abandoned huts.

None of these people wants ever again to hear talk of Renascer, but others continue to fall into the same trap. We spoke to C, too scared to give his full name. A small weather-beaten man of 47 with five children, he is hoping to get a piece of land in Renascer. Like many in Santarém, he migrated to the Amazon from the dirt-poor state of Maranhão, working as a gold miner, sawmill employee and book salesman - whatever turned up. When he heard about the new settlements, he thought it was at last a chance to get land. He eagerly began paying five reals (£1.25) a month to the association of would-be Renascer residents set up by the timber company stooge. Two years have passed; meetings are held, but "nothing happens", says C. "They keep telling us we'll get our plot in two weeks' time . . . I know they're fooling us, but I daren't complain. If I say anything, they'll kill me."

We showed him a photo of Renascer, his first glimpse of his promised land. If these settlers ever get their land, they will be able to survive only with support from the timber companies. But the loggers will leave once they have stripped out all the timber. The community will then collapse and Renascer will be seen as another failed attempt to bring sustainable development to the Amazon. The settlers will be blamed, because the loggers will have airbrushed themselves out of the story.

Near Renascer is another PDS called Santa Clara. This is on a flat plateau - unusual in the Amazon - that is devoid of rivers and streams, and is unsuitable for any kind of settlement because of the risk of forest fires. Yet soya farmers from Mato Grosso have moved in, attracted by cheap (in reality, illegal) land. Cargill has agreed to purchase the soya - no questions asked about origins. Caught unawares by the tougher strategy from Brasilia, the soya farmers have been given hefty fines for clearing virgin forest, but they are determined to stay in the area, even if it means allying themselves with land sharks and corrupt local officials.

Since 2005, almost 100 conservation units of various kinds have been created in the Santarém area. One researcher told us that nine-tenths of them were facades behind which loggers and farmers are hiding. By claiming that their timber and soya come from environmentally sustainable projects, they may even get better prices.

Over the past 30 years, the Amazon has become a byword for violence and lawlessness. As we should have remembered, listening to the head of the forest programme describe his brave new world in Brasilia, technology alone cannot change this. Many government officials have a commitment to stopping the senseless destruction of the forest but, on the ground, corruption, understaffing and inadequate resources undermine their efforts.